This invention relates to spherical plug or ball valves, and more particularly to an improved seat assembly for sealing against the rotatable ball valve member of the ball valve.
Heretofore, ball valves have been provided with rotatable ball valve members mounted within a valve chamber and rotatable between open and closed positions relative to inlet and outlet flow passages communicating with the valve chamber. Further, so-called top entry ball valves have been provided in which a removable top plate covers the valve chamber and is removed for insertion and removal of the ball valve member from the valve chamber. Normally, a valve seat assembly is positioned about each flow passage for sealing against the ball valve member, and the seat assembly is urged to a retracted position when the ball valve member is inserted or removed from the valve chamber.
Such seat assemblies, particularly for top entry ball valves, have normally been provided with elastomeric seat members for sealing against the ball valve member. As well known, an elastomeric seat member will deteriorate at high temperatures above around 300.degree. F. and permit fluid leakage between the inlet and outlet flow passages in the closed position of the ball valve member. For example U.S. Pat. No. 4,477,055 dated Oct. 16, 1984 shows a top entry ball valve having a ball valve member mounted for rotation on trunnions and a retractable seat assembly with an elastomeric sealing member for sealing against the ball valve member.